A trick truckers use to get grease out of our clothes is engine starting fluid (Either.) Just spray it on the grease spot and let it air dry. Once dry, throw in the washer. It is highly flammable so do it outdoors and no open flame. Works like a drycleaner and dissolves the grease like magic.
5th wheels are nasty greasy things but a dry 5th wheel will effect your steering. The thing about grease is you just need a film, not glops of it. If rust would form on the 5th wheel you knew it needed grease. As long as there is a film of grease you are good to go.